Cracking Tumor Defiance

Cracking Tumor Defiance

Reporter: Irina Robu, PhD

Two research groups from Harvard Medical School based at Dana Faber Cancer Institute have discovered a genetic mechanism in a cancer cells that influence whether they respond or resist to immunotherapy drugs, otherwise called as checkpoint inhibitors. The results are published in Science as part of two articles. One article is focused on clinical trial patients with advanced kidney cancer treated with checkpoint inhibitors comes from Eliezer van Allen’s group at Dana Farber Cancer Institute and Toni Choueiri group at Lank Center for Genitourinary Oncology at Dana Farber. The second articles is focused on identifying the immunotherapy resistance mechanism in melanoma cells comes from Kai Wucherpfennig at Dana-Farber and Shirley Liu at Dana -Farber. The two groups joined on that the resistance to immune checkpoint blockade is critically controlled by changes in a group of proteins that regulate how DNA is packaged in cells. The assortment of proteins, called a chromatin remodeling complex, is known as SWI/SNF. Its components are encoded by different genes, among them ARID2, PBRM1 and BRD7. SWI/SNF’s job is to open up stretches of tightly wound DNA so that its blueprints can be read by the cell to activate certain genes to make proteins.

Scientists led by Van Allen and Choueiri wanted a clarification for why some patients with a form of metastatic kidney cancer, clear cell renal carcinoma (ccRCC) gain clinical benefit from treatment with immune checkpoint inhibitors that block the PD-1 checkpoint while others patients don’t. The researchers use whole exome DNA sequencing to analyze tumor samples from 35 patients treated in a clinical trial with Opdivo, a checkpoint blocker nivolumab to search for other characteristics of ccRCC tumors that influence immunotherapy response and/or resistance. The scientist discovered that patients from the trial benefited from the immunotherapy treatment with longer survival and progression free survival were those whose tumors lacked a functioning PRBM1 gene. Loss of PRBM1 gene function caused cancer cells to have increased expression of other genes including those in the gene pathway known as IL6/JAK-STAT3, which is involved in immune system stimulation.

When the PBRM1 gene was knocked out in experiments, the melanoma cells became more sensitive to interferon gamma produced by T cells and, in response, produced signaling molecules that recruited more tumor-fighting T cells into the tumor. The two other genes in the PBAF complex—ARID2 and BRD7—are also found mutated in some cancers, according to the researchers, and those cancers, like the melanoma lacking ARID2 function, may also respond better to checkpoint blockade. According to the researchers, finding ways to alter those target molecules “will be important to extend the benefit of immunotherapy to larger patient populations, including cancers that thus far are refractory to immunotherapy.”